1. Field of Invention
The present invention relates to a respiratory gas sensor which is used for measuring gas concentration in respiratory gas from a living body or determining whether the living body breathes or not, and more particularly to the respiratory gas sensor (hereinafter referred to simply as xe2x80x9ca sensorxe2x80x9d) which is suitable in case where a target to be measured is a living body whose tidal volume is relatively small.
2. Related Art
As an apparatus for measuring the concentration of the gas such as carbon dioxide gas in the expiratory gas from the living body, there has been known such a sensor disclosed in Examined Japanese Utility Model Publication Hei. 4-48534. A structure of this sensor is shown in FIG. 14. FIG. 14 is a sectional view of an essential part showing a function of the sensor in an enlarged scale.
In the drawings, a sensor 1 includes an airway adaptor 2 which is a tubular member, a light source 3 and an infrared detecting portion 4 which are provided on an outer periphery of the airway adaptor 2 at an approximately right angle with respect to an axis of the airway adaptor 2. These light source 3 and infrared detecting portion 4 are provided on a same optical axis so that infrared light passes through the airway adaptor 2 in a direction of an approximately right angle with respect to its axis through optical windows 5, 6 which are airtightly provided in an outer wall of the airway adaptor 2. The infrared detecting portion 4 detects only light having a wavelength which has been absorbed by the gas in the respiratory gas flowing through the airway adaptor 2, such as carbon dioxide gas, and the gas concentration is measured by as known technique.
When the gas concentration is measured by the sensor 1 having the above described structure, in case where an inner volume of the respiratory gas sensor is large, the sensor 1 cannot be used for the living body which has a small tidal volume such as a neonatal and pediatric patient, because its dead space volume is too large. In order to solve this problem, there has been provided, in the publication described above, a tubular adaptor 7 which is fitted with an inner peripheral face of the airway adaptor 2 and formed with a through hole 7a at a position in alignment with the optical windows 5, 6 as shown in FIG. 14. With this structure, the inner volume of the sensor 1 is substantially reduced, and the dead space volume will be decreased. As a result, the concentration of the gas such as carbon dioxide gas in the respiratory gas from the neonatal and pediatric patient who has the small tidal volume can be efficiently measured.
However, in the conventional sensor constructed as above, the respiratory gas flows through a through hole 7b having a small inner diameter in a center part of the adaptor 7, and only a central portion of light which is irradiated from the light source 3 passes through the respiratory gas. For this reason, an amount of the light to be detected by the infrared detecting portion 4 is decreased, resulting in deterioration of measuring accuracy.
Further, the respiratory gas has generally humidity of almost 100%. Therefore, when measurements have been repeated several times, waterdrops caused by humidity gather to be a waterlayer 8, and the waterlayer may remain in the through holes 7a facing the optical windows 5, 6 provided in the adaptor 7 and will not flow out outside, as shown in FIG. 14. As a result, the waterlayer interrupts the light to cause a measurement error.
The invention has been made in view of the above circumstances, and an object of the present invention is to provide a respiratory gas sensor having a simple structure which can efficiently measure the gas concentration in the respiratory gas from the living body which has the small tidal volume, with high accuracy and without an influence caused by the waterdrops and the waterlayer.
In order to attain the above described object, according to an aspect of the present invention, a respiratory gas sensor includes a tubular member including a pathway formed therein, a pair of optical windows formed airtightly in a circumferential wall of the tubular member for allowing light to pass through said optical windows from the exterior into the gas flowing through the pathway, an adaptor fitted to an inner peripheral face of the tubular member and provided with a through hole at a position in alignment with the optical windows, and slits formed in the adaptor in an axis direction in such a manner that the slits face and position adjacent to the optical windows formed on the outer periphery of the tubular member, respectively, and each slit having a width larger than that of the optical window in a direction orthogonal to the axis direction of said pathway.
According to a second aspect of the present invention, as a respiratory gas sensor as mentioned in the first aspect of the present invention, the adaptor is divided in axially opposite sides of the optical windows.
According to a third aspect of the present invention,as a respiratory gas sensor as mentioned in the second aspect of the present invention, the adaptor to be divided is fixed inside the tubular member.
According to a fourth aspect of the present invention, as a respiratory gas sensor as mentioned in the second aspect of he present invention, the adaptor to be divided is detachably connected with each other inside the tubular member.
According to a fifth aspect of the present invention, as a respiratory gas sensor as mentioned in the first to fourth aspects of the present invention, anti-fogging films are provided on inner faces of the optical windows.
According to a sixth aspect of the present invention, there is provided a respiratory gas sensor including a tubular member including a pathway formed therein, and a pair of optical windows formed airtightly in a peripheral wall of the tubular member for allowing light to pass through said optical windows from the exterior into the gas flowing through the pathway, a partitioning portion for dividing the pathway into plurality of passages, the partitioning portion including a through hole for allowing light to pass through from one of the optical windows to the other, the passages divided by the partitioning portion being adapted to extend along the optical windows respectively and each having a width larger than that of each of the optical windows in a direction orthogonal to the pathway
According to a seventh aspect of the present invention, as a respiratory gas sensor as mentioned in the sixth aspect of the present invention, anti-fogging films are provided on inner faces of the optical windows.
According to the present invention, the adaptor is formed with the slits on its outer periphery at positions respectively facing with and adjacent to the optical windows in an axial direction along the entire length of the adaptor, each of the slits having a width larger than that of each of the optical windows in a direction orthogonal to the axis direction of said pathway. Therefore, the whole light generated from the light source and passing through the optical windows can irradiate the respiratory gas which passes through the pathway and the concentration of the gas can be measured efficiently and with high accuracy. Further, as the slits are formed in adjacent to the optical windows, the waterdrops will not remain on the inner faces of the optical windows.
According to the second to fourth aspects of the present invention, the adaptor is divided so that a molding operation can be simply subjected. In this case, the adaptor to be divided may be fixed to the tubular member or detachably connected thereto. By constructing the adaptor to be detachable, the adaptor can be taken out from the tubular member after the use, then cleaned and sterilized to be reusable.
According to the fifth aspect of the present invention, the anti-fogging films are provided on the inner faces of the optical windows, thereby preventing the inner faces of the optical windows from fogging by humidity of the respiratory gas which passes through the slits.
According to the sixth aspect of the present invention, there is achieved to a similar function to the first aspect of the present invention.
According to the seventh aspect of the present invention, there is achieved to a similar function to the fifth aspect of the present invention.